I have just taken the plunge into the 1/72 plastic pool and finished my first Sapanish unit using HaT 1806 Prussians with a few 1805 French thrown in. The bases are made of card with 1 pence piece fillers to add some weight.
The method I used was to washed first and then spray with Rustoleum White primer. This is now available in the UK from B+Q. I used a light grey ink and Johnsons floor wash (the UK version of Future) mixed with warter and used acrylic inks for much of the equipment and unit facings. This is so easy to use as it is a flows and stains the colour on. If using Inks do not use any more Future as this will and lifts the ink and it will run
all over the figure. I just used Rowney Acrylic matt varnish to finish.
In all I painted 38 figures in about 5 hours - which is way quicker than my nornal painting time.
The biggest issue you will find is that many wargamers look down on plastic figures as some sort of inferior product. In my group 2 reject the idea of plastic out of hand where as along with 2 others we are now embarking on a doing the WSS using Zvezda GNW figures. See next post for photos